The present invention relates to a distributing roller unit and a printing mechanism provided therewith.
Printing machines having inking rollers, dampening rollers and distributing rollers are widely known. German Offenlegungsschrift 2,845,932 discloses an offset printing mechanism having a combined inking and dampening mechanism with a friction-driven axially movable intermediate roller which connects the inking and dampening mechanism in a unit. In this construction, the intermediate roller is arranged fixedly. This possesses considerable disadvantages in the fact that, because of the fixed arrangement of the intermediate roller, its switching can be performed only in connection with the inking rollers, whereby an optimal removal of interference screens from inking and damping interference stencils cannot be differentially performed.
The screening stenciling is a phenomenon when the formation of one point of the printing form takes place at a location which is different from the location desired and lies in a circumferential direction at an application roller projection behind the first point. In other words, the printing plate includes printing and non-printing surface portions, wherein from the non-printing surface portions of the printing plate no ink is taken from the application roller and thereby an ink accumulation on the application roller takes place, which during rotation of the application roller is applied on the printing press with offset and therefore leads to undesired stripe or stencil formation. This phenomenon is increased by the plate cylinder channel, which forms a print-free zone and thereby no printing ink is taken which is then applied with offset from the application roller onto the print carrier. The above presented information with respect to the inking roller is completely applicable with respect to the dampening roller. The moisture concentration on the dampening roller leads with the printing ink to emulsification, and in some cases to ink disturbance. This phenomenon is called by experts "ghosting" or "ghost image" and identified as interference in the application. It also can be called inking and dampening interference stencils, since a certain overlapping of ink and dampening substance at not desired positions leads to the above mentioned quality failure on the printed sheets.